1. Field of the Invention
The present invention relates to an electrophotographic apparatus.
2. Description of the Related Art
An electrophotographic apparatus is widely used, for instance, for a copying machine, a facsimile and a printer. In addition, as an electrophotographic photosensitive member which is used for the electrophotographic apparatus, an electrophotographic photosensitive member having a photoconductive layer (photosensitive layer) formed from amorphous silicon thereon (amorphous-silicon electrophotographic photosensitive member) is well known.
FIG. 2 is a view illustrating an example of a conventional electrophotographic apparatus having a heater for an electrophotographic photosensitive member.
In the electrophotographic apparatus illustrated in FIG. 2, an electrophotographic photosensitive member 2001 has a heater 2010 for an electrophotographic photosensitive member installed therein, and the heater controls the surface temperature of the electrophotographic photosensitive member 2001.
In FIG. 2, the surface of the electrophotographic photosensitive member 2001 which is rotationally driven toward the direction of the arrow is electrostatically charged by a charging device 2002. The charging potential of the surface of the electrophotographic photosensitive member 2001 is adjusted by an electric current value which is passed to a charging wire 2011 in the charging device 2002. Subsequently, the surface of the electrophotographic photosensitive member 2001 is irradiated with an image exposure beam 2003 emitted from an image exposure device (not shown), and an electrostatic latent image is formed on the surface thereof. Then, the electrostatic latent image which has been formed on the surface of the electrophotographic photosensitive member 2001 is developed by a toner which is supplied from a developing device 2004, and a toner image is formed on the surface of the electrophotographic photosensitive member 2001.
After that, the toner image which has been formed on the surface of the electrophotographic photosensitive member 2001 is transferred onto a transfer material 2006 by a transfer device 2005. Subsequently, the transfer material 2006 is separated from the surface of the electrophotographic photosensitive member 2001, and then the toner image which has been transferred onto the transfer material 2006 is fixed on the transfer material 2006 by a fixing device (not shown).
On the other hand, a toner which has remained on the surface of the electrophotographic photosensitive member 2001 without having been transferred onto the transfer material 2006 is removed by a cleaning blade 2008 in a cleaning device 2007.
Subsequently, a pre-exposing device (not shown) irradiates the surface of the electrophotographic photosensitive member 2001 with pre-exposure light 2009, and the surface of the electrophotographic photosensitive member 2001 is electrostatically discharged.
Images are continuously formed (image output) by the repetition of the above series of processes.
In recent years, an opportunity of outputting an image such as a photograph and a picture by using the electrophotographic apparatus has increased, and as a result, a requirement for an electrophotographic image to have a higher image quality has increased. The unevenness of image density (nonuniformity of image density) in particular can be easily discriminated by human eyes, and accordingly a requirement for the reduction of the unevenness of the image density has particularly increased.
One factor which causes the unevenness of the image density includes the unevenness (nonuniformity) of photosensitive-member characteristics such as charging characteristics and sensitivity characteristics of the electrophotographic photosensitive member. The unevenness of the photosensitive-member characteristics originates in the unevenness (nonuniformity) of film quality and film thickness of the film which constitutes the electrophotographic photosensitive member, in many cases.
In recent years, along with the improvement of a method for manufacturing an electrophotographic photosensitive member, the unevenness of the film quality and the film thickness of the film which constitutes the electrophotographic photosensitive member has been progressively reduced, and as a result, the unevenness of the image density has also been progressively reduced.
In addition, Japanese Patent Application Laid-Open No. H07-209930 discloses a technology of arranging a plurality of heating units in the inside of an electrophotographic photosensitive member, controlling temperatures of each of the heating units, and thereby suppressing the unevenness of the image density.
In recent years, it is required for the electrophotographic apparatus not only to form an image of high quality but also to save power from the viewpoint of environmental consideration, and an electrophotographic apparatus having no heater for an electrophotographic photosensitive member is desired.
However, there is the case in which the electrophotographic apparatus having no unit for controlling the surface temperature of the electrophotographic photosensitive member, such as the heater for the electrophotographic photosensitive member, cannot sufficiently control the unevenness of the image density, and under present circumstances, the electrophotographic apparatus still has room to be improved.